Method for treating intervertebral disc degeneration

ABSTRACT

A percutaneous method treats degenerate disc disease characterized by a circumferential bulge. The method provides a catheter having a distal end, a proximal end, and a longitudinal axis, the distal end having an intradiscal section with at least one energy delivery device. The next step is applying a force longitudinally to the proximal end of the catheter which is sufficient to advance the intradiscal section through a nucleus pulposus and around an inner wall of an annulus, but which force is insufficient for the intradiscal section to puncture the annulus fibrosus. Next the energy delivery device is positioned at a selected location of the annulus by advancing or retracting the catheter and optionally twisting the proximal end of the catheter. The thermal energy delivery device is positioned adjacent the annulus and used to heat and stiffen the disc. Optionally, there is an additional step of adding a substance to reinforce the area. Optionally, access to the disc is provided by an introducer having an introducer lumen with an opening at a terminus of the introducer. An externally guidable intervertebral disc apparatus also is disclosed.

REFERENCES TO PARENT AND CO-PENDING APPLICATIONS

This application is a continuation of U.S. application Ser. Nos. 08/881,525, 08/881,527, 08/881,692, 08/881,693 filed Jun. 24, 1997, which each claims priority to U.S. Provisional application Ser. Nos. 60/047,820, 60/047,841, 60/047,818, 60/047,848 filed May 28, 1997, U.S. Provisional application Ser. No. 60/045,941 filed May 8, 1997, and U.S. Provisional application Ser. Nos. 60/029,734, 60/029,735, 60/029,600, 60/029,602 filed Oct. 23, 1996 application Ser. Nos. 08/881,525, 08/881,527, 08/881,692, 08/881,693, 60/029,602, 60/029,734, 60/047,848 are each incorporated herein by reference.

BACKGROUND

1. Field of the Invention

This invention relates to methods and apparatuses for modifying intervertebral disc tissue and more particularly to the treatment of circumferential disc rolls, bulges or protrusions using percutaneous disc techniques to avoid major surgical intervention.

2. Description of Related Art

Intervertebral disc abnormalities have a high incidence in the population and may result in pain and discomfort if the disc impinges on or irritates nerves. Disc abnormalities may be the result of trauma, repetitive use, metabolic disorders and the aging process and include such disorders as, but are not limited to, degenerative discs with (i) localized tears or fissures in the annulus fibrosus, (ii) localized disc herniations with contained extrusions, and (iii) chronic, circumferential bulging disc.

Disc fissures and tears result from structural degeneration (a part of the aging process that may be accelerated by trauma) of fibrous components of the annulus fibrosus. Even sneezing, bending or just attrition can separate these degenerated annulus fibers, creating a fissure. The fissure may or may not be accompanied by extrusion of nucleus pulposus material into and beyond the annulus fibrosus. The fissure itself may be the sole morphological change, above and beyond generalized degenerative changes in the connective tissue of the disc. Biochemicals contained within the nucleus pulposus are alleged to escape through the fissure and irritate nearby structures. Disc fissures can be debilitatingly painful. The fissure also may be associated with a herniation of the annulus.

With a contained disc herniation, the nucleus pulposus may work its way partly through the annulus but is still contained within the annulus or beneath the posterior longitudinal ligament, and there are no free nucleus fragments in the spinal canal. Nevertheless, even a contained disc herniation is problematic because the outward protrusion can press on the spinal nerves or irritate other structures.

Another disc problem occurs when the disc bulges outward circumferentially in all directions and not just in one location. This occurs when over time, the disc weakens, bulges outward and takes on a "roll" shape. Mechanical stiffness of the joint is reduced and the joint may become unstable. One vertebra may eventually settle on top of another. This problem continues as the body ages and accounts for shortened stature in old age. With the increasing life expectancy of the population, such degenerative disc disease and impairment of nerve function are becoming major public health problems. As the disc "roll" extends beyond the normal circumference, the disc height may be compromised, and foramina with nerve roots are compressed. In addition, osteophytes may form on the outer surface of the disc roll and further encroach on the spinal canal and foramina through which nerves pass. This condition is called lumbar spondylosis.

It has been thought that such disc degeneration creates pain predominantly via segmental instability which disturbs sensitive structures which register pain. Traditional, conservative methods of treatment include bed rest, pain and muscle relaxant medication, physical therapy or steroid injection. Upon failure of conservative therapy, spinal pain (assumed to be due to instability) has been treated by spinal fusion, with or without instrumentation, which causes the vertebrae above and below the disc to grow solidly together and form a single, solid piece of bone. The procedure is carried out with or without discectomy. Other treatments include discectomy alone or disc decompression with or without fusion. Current treatment methods symptomatic disc rolls include laminectomy or fusion to reduce pressure on the annulus, and nuclectomy to remove some of the interior nucleus pulposus and decrease outward pressure on the annulus. Surgical complications include disc space infection, nerve root injury, hematoma formation, and instability of adjacent vertebrae.

These interventions have been problematic in that alleviation of back pain is unpredictable even if surgery appears successful. In attempts to overcome these difficulties, new fixation devices have been introduced to the market, including but not limited to pedicle screws and interbody fusion cages. Although pedicle screws provide a high fusion success rate, there is still no direct correlation between fusion success rate and patient improvement in function and pain. Studies on fusion have demonstrated success rates of between 50% and 67% for pain improvement, and a significant number of patients have more pain postoperatively. Therefore, different methods of helping patients with degenerative disc problems need to be explored.

FIGS. 1(a) and 1(b) illustrate a cross-sectional anatomical view of a vertebra and associated disc and a lateral view of a portion of a lumbar and thoracic spine, respectively. Structures of a typical cervical vertebra (superior aspect) are shown in FIG. 1(a): 104--lamina; 106--spinal cord; 108--dorsal root of spinal nerve; 114--ventral root of spinal nerve; 116--posterior longitudinal ligament; 118--intervertebral disc; 120--nucleus pulposus; 122--annulus fibrosus; 124--anterior longitudinal ligament; 126--vertebral body; 128--pedicle; 130--vertebral artery; 132--vertebral veins; 134--superior articular facet; 136--posterior lateral portion of the annulus; 138--posterior medial portion of the annulus; and 142--spinous process. In FIG. 1(a), one side of the intervertebral disc 118 is not shown so that the anterior vertebral body 126 can be seen. FIG. 1(b) is a lateral aspect of the lower portion of a typical spinal column showing the entire lumbar region and part of the thoracic region and displaying the following structures: 118--intervertebral disc; 126--vertebral body; 142--spinous process; 170--inferior vertebral notch; 110--spinal nerve; 174--superior articular process; 176--lumbar curvature; and 180--sacrum.

The presence of the spinal cord and the posterior portion of the vertebral body, including the spinous process, and superior and inferior articular processes, prohibit introduction of a needle or trocar from a directly posterior position. This is important because annular tears, herniations and circumferential bulges with or without disc protrusions or extrusions in the posterior disc wall compress or irritate the spinal cord and/or spinal nerves. The inferior articular process 168, along with the pedicle 128 and the spinal nerve 172, form a small "triangular" window (shown in black in FIG. 1(c)) through which introduction can be achieved from the posterior lateral position. This approach is also shown from above in FIG. 1(d). It is well known to those skilled in the art that percutaneous disc access is achieved by placing an introducer into the disc from this posterior lateral approach, but the triangular window does not allow much room to maneuver. Once the introducer pierces the tough annulus fibrosus, the introducer is fixed in two places along its length and has little freedom of movement. Thus, this approach has allowed access only to small portions of the central and anterior portions of the nucleus pulposus. Current methods do not permit percutaneous access to the posterior half of the nucleus or to the posterior wall of the disc. Major and potentially dangerous surgery would be required to access these areas.

U.S. Pat. No. 5,433,739 (the "'739 patent") discloses placement of an RF electrode in an interior region of the disc approximately at the center of the disc. RF power is applied, and heat then putatively spreads out globally throughout the disc. The '739 patent teaches the use of a rigid shaft which includes a sharpened distal end that penetrates through the annulus fibrosus and into the nucleus pulposus. In one embodiment the shaft has to be rigid enough to permit the distal end of the RF electrode to pierce the annulus fibrosus, and the ability to maneuver its distal end within the nucleus pulposus is limited. In another embodiment, a somewhat more flexible shaft is disclosed. However, the embodiments of the '739 patent do not permit access to the posterior, posterior lateral and posterior medial region of the disc, nor do they provide for focal delivery of thermal therapy to a selected local region within the disc or precise temperature control at the annulus. The '739 patent teaches the relief of pain by globally heating the disc. There is no disclosure of repairing the disc.

U.S. Pat. No. 5,201,729 (the "'729 patent") discloses the use of an optical fiber that is introduced into a nucleus pulposus. In the '729 patent, the distal end of a stiff optical fiber shaft extends in a lateral direction relative to a longitudinal axis of an introducer. This prevents delivery of coherent energy into the nucleus pulposus in the direction of the longitudinal axis of the introducer. Due to the limited access from the posterior lateral approach, stiff shaft and lateral energy delivery, the device of the '729 patent is unable to gain close proximity to selected portion of the annulus (posterior, posterior medial and central posterior) requiring treatment or to precisely control the temperature at the annulus. The '729 patent teaches the use of coherent energy to vaporize the nucleus pulposus, which by the nature of the technique generates very high temperatures. No use in repairing the disc is disclosed.

Accordingly, it is desirable to diagnose and treat disc degeneration at locations previously not accessible via percutaneous approaches without substantial destruction to the disc. It would be further desirable to provide controlled thermal energy to collagen in the degenerated locations to tighten and stiffen the annulus, particularly at the posterior, posterior lateral and the posterior medial regions of the annulus fibrosus. It would further be desirable to be able to administer materials to a precise, selected location within the disc, for example, to the locations requiring reinforcement of the degenerated disc.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a minimally invasive method and apparatus for diagnosing and treating degenerative discs, particularly the circumferential bulging that results from degeneration of the annulus fibrosus.

Another object of the invention is to provide an apparatus which is advanceable and guidable adjacent to the inner wall of the annulus fibrosus to concentrate and control treatment at the annulus.

Still a further object of the invention is to provide a device which has a distal end that is inserted into the disc and accesses all the circumference of the inner wall of the annulus fibrosus in order to controllably heat and shrink or stiffen the annulus.

These and other objects of the invention have been accomplished by the present invention which provides methods for treating intervertebral disc disease such as degenerative discs with a circumferential bulge. The method comprises providing a catheter having a distal end, a proximal end and a longitudinal axis, the proximal end having an intradiscal section with at least one thermal energy delivery device; applying a force longitudinally to the proximal end of the catheter sufficient to advance the intradiscal section through the nucleus pulposus and around the inner wall of the annulus fibrosus, but which force is insufficient to puncture the annulus fibrosus, which results in positioning the energy delivery device at a selected location on the annulus; and causing the energy delivery device to supply sufficient energy at the selected location to stiffen the annulus.

In addition to the method, there is also provided an externally guidable intervertebral disc apparatus for treatment of degenerate circumferential disc bulges. The apparatus comprises a catheter having a distal end, a proximal end, and a longitudinal axis, the distal end having an intradiscal section, the intradiscal section being extendible into the disc and having sufficient rigidity to be advanceable through the nucleus pulposus of the disc and around the inner wall of the annulus fibrosus under a force applied longitudinally to the proximal end and having insufficient penetration ability to be advanceable out through the annulus fibrosus under the applied force; and at least one energy delivery device located in the intradiscal section for applying energy at the selected location within the disc.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood by reference to the following figures that form part of the current specification, wherein:

FIG. 1(a) is a superior cross-sectional anatomical view of a cervical disc and vertebra.

FIG. 1(b) is a lateral anatomical view of a portion of a lumbar spine.

FIG. 1(c) is a posterior-lateral anatomical view of two lumbar vertebrae and illustration of the triangular working zone.

FIG. 1(d) is a superior cross-sectional view of the required posterior lateral approach.

FIG. 2 is a second cross-sectional view of an intervertebral disc illustrating a disc plane of the intervertebral disc and an oblique cephalo-caudad plane.

FIG. 3(a) is a plan view of an introducer and an instrument of the invention in which solid lines illustrate the position of the instrument in the absence of bending forces and dotted lines indicate the position the distal portion of the instruments would assume under bending forces applied to the intradiscal section of the instrument.

FIG. 3(b) is an end view of the handle of the embodiment shown in FIG. 3(a).

FIG. 4 is a cross-sectional view of an intervertebral disc with a portion of the intervertebral apparatus of the present invention inserted in the intervertebral disc.

FIG. 5(a) is a cross-sectional view of the intervertebral segment of the embodiment of the invention shown in FIG. 3(a) taken along the line 5(a)-5(a) of FIG. 3(a).

FIG. 5(b) is a cross-sectional view of the intervertebral segment of a second embodiment of the present invention having a combined wall/guiding mandrel.

FIG. 6 is a perspective view of an embodiment of an apparatus of the present invention with a resistive heating coil positioned around an exterior of an intradiscal section of the catheter.

FIG. 7 is a partial cross-sectional view of an embodiment an apparatus of the invention illustrating a sensor positioned in an interior of the intradiscal section of the catheter.

FIG. 8 is a partial cross-sectional view of an embodiment of the apparatus of the invention further including a sheath positioned around the resistive heating coil.

FIG. 9 is a partial cross-sectional view of an embodiment of the apparatus of FIG. 6 with multiple resistive heating coils.

FIG. 10 is a plan view of an embodiment of the intradiscal section of a catheter of the invention with a helical structure.

FIG. 11 is a block diagram of an open or closed loop feedback system that couples one or more sensors to an energy source.

FIG. 12 is a block diagram of an embodiment illustrating an analog amplifier, analog multiplexer and microprocessor used with the feedback control system of FIG. 11.

The invention now being generally described, the same will be better understood by reference to the following detailed description of specific embodiments and general features of the invention.

DETAILED DESCRIPTION

The present invention provides a method and apparatus for treating degenerative disc disorders, particular circumferential bulges in the annulus fibrosus.

In general, an apparatus of the invention is in the form of an externally guidable intervertebral disc apparatus for accessing and manipulating degenerate disc tissue at a selected location. Use of a temperature-controlled energy delivery element, combined with the positional control of the catheter of the invention, allows preferential, local heating within the disc. For ease of reference to various manipulations and distances described below, the nucleus pulposus can be considered as having a given diameter in a disc plane between opposing sections of the inner wall. This nucleus pulposus diameter measurement allows instrument sizes (and parts of instruments) designed for one size disc to be readily converted to sizes suitable for an instrument designed for a different size of disc.

The operational portion of the apparatus of the invention is brought to a location in or near the disc's bulge using techniques and apparatuses typical of percutaneous interventions. For convenience and to indicate that the apparatus of the invention can be used with any insertional apparatus that provides proximity to the disc, including many such insertional apparatuses known in the art, the term "introducer" is used to describe this aid to the method. An introducer has an internal introducer lumen with a distal opening at a terminus of the introducer to allow insertion (and manipulation) of the operational parts of the apparatus into (and in) the interior of a disc.

The operational part of the apparatus comprises an elongated element referred to as a catheter, various parts of which are located by reference to a distal end and a proximal end at opposite ends of its longitudinal axis. The proximal end is the end closest to the external environment surrounding the patient's body (which may still be inside the body in some embodiments if the catheter is attached to a handle insertable into the introducer). The distal end of the catheter is intended to be located inside the disc under conditions of use. The catheter is not necessarily a traditional medical catheter (i.e., an elongate hollow tube for admission or removal of fluids from an internal body cavity) but is a defined term for the purposes of this specification. "Catheter" has been selected as the operant word to describe this part of the apparatus, as the apparatus is a long, flexible tube which transmits energy and/or material from a location external to the body to a location internal to the disc being accessed upon, such as a collagen solution, and heat to the annular degeneration. Alternatively, material can be transported in the other direction to remove material from the disc, such as removing material by aspiration to decrease pressure in the disc, which is aggravating the patient's symptoms.

The catheter is adapted to slidably advance through the introducer lumen, the catheter having an intradiscal section at the distal end of the catheter, the intradiscal section being extendible through the distal opening at the terminus of the introducer into the disc. Although the length of the intradiscal portion can vary with the intended function as explained in detail below, a typical distance of extension is at least one-half the diameter of the nucleus pulposus, preferably in the range of one-half to one and one-half times the circumference of the nucleus.

In order that the functional elements of the catheter can be readily guided to the desired location within a disc, the intradiscal portion of the catheter is manufactured with sufficient rigidity to avoid collapsing upon itself while being advanced through the nucleus pulposus and navigating around the inner wall of the annulus fibrosus. The intradiscal portion, however, has insufficient rigidity to puncture the annulus fibrosus under the same force used to advance the catheter through the nucleus pulposus and navigate around the inner wall of the annulus fibrosus. Absolute penetration ability will vary with sharpness and stiffness of the tip of the catheter, but in all cases a catheter of the present invention will advance more readily through the nucleus pulposus than through the annulus fibrosus.

In preferred embodiments, the intradiscal section of the catheter further has differential bending ability in two orthogonal directions at right angles to the longitudinal axis. This causes the catheter to bend along a desired plane (instead of at random), usually around the annulus fibrosus. Also when a torsional (twisting) force is applied to the proximal end of the catheter, the distal end of the catheter is re-oriented for controlled navigation of the catheter in the desired plane.

A further component of the catheter is a functional element located in the intradiscal section for diagnosis or for adding energy and adding and/or removing material at the selected location of the disc where the annular tear is to be treated. The apparatus allows the therapeutic device to be controllably guided by manipulation of the proximal end of the catheter into a selected location for localized treatment of the degenerate annulus.

The method of the invention, which involves manipulating disc tissue at the annulus fibrosus, is easily carried out with an apparatus of the invention. An introducer is provided that is located in a patient's body so that its proximal end is external to the body and the distal opening of its lumen is internal to the body and internal to the annulus fibrosus. The catheter is then slid into position in and through the introducer lumen so that the functional element in the catheter is positioned at the selected location of the disc by advancing or retracting the catheter in the introducer lumen and optionally twisting the proximal end of the catheter to precisely navigate the catheter. By careful selection of the rigidity of the catheter and by making it sufficiently blunt to not penetrate the annulus fibrosus, and by careful selection of the flexibility in one plane versus the orthogonal plane, the distal portion of the catheter will curve along the inner wall of the annulus fibrosus as it is advanced and is selectively guided to degenerate disc at location(s) in the disc. Energy is applied and/or material is added or removed at selected locations of the disc via the functional element.

Each of the elements of the apparatus and method will now be described in more detail. However, a brief description of disc anatomy is provided first, as sizes and orientation of structural elements of the apparatus and operations of the method can be better understood in some cases by reference to disc anatomy.

The annulus fibrosus is comprised primarily of tough fibrous material, while the nucleus pulposus is comprised primarily of an amorphous colloidal gel. There is often a transition zone between the annulus fibrosus and the nucleus pulposus made of both fibrous-like material and amorphous colloidal gel. The border between the annulus fibrosus and the nucleus pulposus becomes more difficult to distinguish as a patient ages, due to degenerative changes. This process may begin as early as 30 years of age. For purposes of this specification, the inner wall of the annulus fibrosus can include the young wall comprised primarily of fibrous material as well as the transition zone which includes both fibrous material and amorphous colloidal gels (hereafter collectively referred to as the "inner wall of the annulus fibrosus"). Functionally, that location at which there is an increase in resistance to catheter penetration and which is sufficient to cause bending of the distal portion of the catheter into a radius less than that of the internal wall of the annulus fibrosus is considered to be the "inner wall of the annulus fibrosus".

As with any medical instrument and method, not all patients can be treated, especially when their disease or injury is too severe. There is a medical gradation of degenerative disc disease (Stages 1-5). See, for example, Adams et al., "The Stages of Disc Degeneration as Revealed by Discograms," J. Bone and Joint Surgery, 68, 36-41 (1986). As these grades are commonly understood, the methods of instrument navigation described herein would probably not be able to distinguish between the nucleus and the annulus in degenerative disease of grade 5. In any case, most treatment is expected to be performed in discs in stages 3 and 4, as stages 1 and 2 are asymptomatic in most patients, and stage 5 may require disc removal and fusion.

Some of the following discussion refers to motion of the catheter inside the disc by use of the terms "disc plane," "oblique plane" or "cephalo-caudal plane." These specific terms refer to orientations of the device relative to the intervertebral disc. Referring now to FIG. 2 (which shows a vertical cross-section of a disc), a disc plane 30 of the intervertebral disc is generally a plane of some thickness 27 within the nucleus pulposus 120 orthogonal to the axis formed by the spinal column (i.e., such a disc plane would be substantially horizontal in a standing human, corresponding to the "flat" surface of a vertebra. An oblique plane 31 extends along any tilted orientation relative to axial plane 30. However, when the plane is tilted at 90°, such a plane would be substantially vertical in a standing human, and is referred to as a cephalo-caudal plane. Reference is made to such planes to describe device orientations away from the disc plane. In various embodiments, disc plane 30 has a thickness no greater than the thickness of the intervertebral disc, preferably a thickness no greater than 75% of a thickness of the intervertebral disc, and more preferably a thickness no greater than 50% of a thickness of the intervertebral disc. Movement of the intradiscal portion 16 of catheter 14 is confined within a disc plane by the physical and mechanical properties of the intradiscal portion 16 during advancement of the catheter when the bending plane of the catheter is aligned with the disc plane, until some additional force is applied to the catheter by the physician. A twisting force (which can be applied mechanically, electrically, or by any other means) acting on the proximal end of the catheter changes the forces acting on the distal end of the catheter so that the plane of the catheter bend can be angled relative to the disc plane as the catheter is advanced. Thus, the distal end of the catheter can be moved up or down (depending on the direction of the twist) within the intervertebral disc under the control of the physician.

Turning now to the introducer, a detailed description of an entire apparatus should not be necessary for those skilled in the art of percutaneous disc procedures and the design of instruments intended for such use. The method of the invention can also be carried out with endoscopic instruments, and an endoscopic apparatus having structural parts that meet the descriptions set forth in this specification would also be an apparatus for the delivery of the invention.

In general, a device of the invention can be prepared in a number of different forms and can consist (for example) of a single instrument with multiple internal parts or a series of instruments that can be replaceably and sequentially inserted into a hollow fixed instrument (such as a needle or endoscope) that guides the operational instruments to a selected location in or adjacent to annular degeneration. Because prior patents do not fully agree on how to describe parts of percutaneous instruments, terminology with the widest common usage will be used.

The introducer, in its simplest form, can consist of a hollow needle-like device (optionally fitted with an internal removable obturator or trocar to prevent clogging during initial insertion) or a combination of a simple exterior cannula that fits around a trocar. The result is essentially the same: placement of a hollow tube (the needle or exterior cannula after removal of the obturator or trocar, respectively) through skin and tissue to provide access into the annulus fibrosus. The hollow introducer acts as a guide for introducing instrumentation. More complex variations exist in percutaneous instruments designed for other parts of the body and can be applied to design of instruments intended for disc operations. Examples of such obturators are well known in the art. A particularly preferred introducer is a 17- or 18-gauge, thin-wall needle with a matched obturator, which after insertion is replaced with a catheter of the present invention.

Referring now to the figures, FIGS. 3(a) and 3(b) illustrate one embodiment of a catheter 14 of the invention as it would appear inserted into an introducer 12. The apparatus shown is not to scale, as an exemplary apparatus (as will be clear from the device dimensions below) would be relatively longer and thinner; the proportions used in FIG. 3(a) were selected for easier viewing by the reader. The distal portion of an intervertebral apparatus operates inside an introducer 12 having an internal introducer lumen 13. A flexible, movable catheter 14 is at least partially positionable in the introducer lumen 13. Catheter 14 includes a distal end section 16 referred to as the intradiscal section, which is designed to be the portion of the catheter that will be pushed out of the introducer lumen and into the nucleus pulposus, where movement of the catheter will be controlled to bring operational portions of the catheter into the proper location with regard to the annular tear. In FIG. 3(a), dashed lines are used to illustrate bending of the intradiscal portion of the catheter as it might appear under use, as discussed in detail later in the specification. FIG. 3(b) shows an end view of handle 11 at the proximal end of the catheter, with the handle 11 having an oval shape to indicate the plane of bending, also discussed in detail later in the specification. Other sections and properties of catheter 14 are described later.

For one embodiment suitable for intervertebral discs, the outer diameter of catheter 14 is in the range of 0.2 to 5 mm, the total length of catheter 14 (including the portion inside the introducer) is in the range of 12 to 60 cm, and the length of introducer 12 is in the range of 5 to 50 cm. For one preferred embodiment, the catheter has a diameter of 1 mm, an overall length of 30 cm, and an introduced length of 15 cm (for the intradiscal section). With an instrument of this size, a physician can insert the catheter for a distance sufficient to reach any selected location in the nucleus of a human intervertebral disc.

FIG. 4 illustrates the anatomy of an intervertebral disc and shows an apparatus of the invention inserted into a disc. Structures of the disc are identified and described by these anatomical designations: the posterior lateral inner annulus 136, posterior medial inner annulus 138, annulus fibrosus 122/nucleus pulposus 120 interface, the annulus/dural interface 146, annulus/posterior longitudinal ligament interface 148, anterior lateral inner annulus 150, and the anterior medial inner annulus 152.

Referring again to FIG. 4, the mechanical characteristics of intradiscal section 16 of catheter 14 are selected to have (1) sufficient column strength along the longitudinal axis of the catheter to avoid collapse of the catheter and (2) different flexural strengths along the two axes orthogonal to the longitudinal axis to allow controlled bending of the catheter. These parameters make the catheter conformable and guidable along inner wall 22 of an annulus fibrosus 122 to reach selected locations, such as the posterior medial annulus 138.

Specific mechanical characteristics of particular designs will be described later in the examples that follow. Generally, however, the necessary design features can be selected (in an interrelated fashion) by first providing the intradiscal section of the catheter with sufficient column strength to be advanceable through normal human nucleus pulposus and navigable around the inner wall of the annulus fibrosus without collapse. Here "collapse" refers to bending sufficient to inhibit further advancement at the tip. Advancement of the tip is impeded by resistance from 1) advancing through the normal gelatinous nucleus pulposus, 2) contacting denser clumps of nucleus pulposus and 3) navigating along the arc of the inner wall of the annulus. Column strength can be increased in many ways known in the art, including but not limited to selecting a material (e.g., metal alloy or plastic) with a high resistance to bending from which to form the catheter, forming the structure of the catheter with elements that add stiffening (such as bracing), and increasing the thickness of the structural materials. Column strength can be decreased to favor bending by selecting the opposite characteristics (e.g., soft alloys, hinging, and thin structural elements).

When the catheter collapses, the physician feels an abrupt decrease in resistance. At that time, the catheter forms one or more loops or kinks between the tip of the introducer and the distal tip of the catheter.

Particularly preferred for treating the posterior of the annulus, the tip 28 of intradiscal section 16 is biased or otherwise manufactured so that it forms a pre-bent segment prior to contact with the annulus fibrosus as shown in FIG. 3(a). The bent tip will cause the intradiscal section to tend to continue to bend the catheter in the same direction as the catheter is advanced. This enhanced curving of a pre-bent catheter is preferred for a catheter that is designed to reach a posterior region of the nucleus pulposus; however, such a catheter must have sufficient column strength to prevent the catheter from collapsing back on itself.

The intradiscal section not only must allow bending around the relatively stronger annulus fibrosus in one direction, but also resist bending in the orthogonal direction to the desired plane. By twisting the proximal end of a catheter and thus controlling the orientation of the plane of bending while concurrently controlling the advancement of the catheter into the nucleus, a physician can navigate the catheter and its instrumentation within the disc.

The bending stiffness of the intradiscal section as measured in Taber stiffness units (using a length of the inventive catheter as the test strip rather than the standard dimension, homogeneous-material test strip) should be in the range of 2-400 units (in a 0-10,000 unit range) in the desired bending plane, preferably 3-150 units. In preferred embodiments, stiffness is in the range of 4-30 units in the desired bending plane. In all cases, the bending stiffness preferably is 2-20 times higher for bending in the orthogonal direction.

The column or compressive strength of the intradiscal section (force required to buckle a segment whose length is 25 or more times its diameter) is in the range of 0.05 to 4 kg, preferably 0.1 to 2 kg. In the most preferred embodiments, it is in the range of 0.1 to 1 kg. In the proximal shaft section (i.e., the part of the catheter proximal to the intradiscal section), this strength is in the range of 0.1 to 25 kg, preferably 0.2 to 7 kg. In the most preferred embodiments, it is in the range of 0.7 to 4 kg.

Returning now to FIG. 4, intradiscal section 16 is guidable and can reach the posterior, the posterior lateral, and the posterior medial regions of the posterior wall of the annulus fibrosus, as well as other selected section(s) on or adjacent to inner wall 22. In order to move the functional section of the catheter into a desired nucleus location, intradiscal section 16 is first positioned in the nucleus pulposus 120 by means of the introducer.

In most uses, introducer 12 pierces annulus fibrosus 122 and is advanced through the wall of the annulus fibrosus into the nucleus pulposus. In such embodiments, introducer 12 is then extended a desired distance into nucleus pulposus 120. Catheter 14 is advanced through a distal end of introducer 12 into nucleus pulposus 120. Advancement of the catheter 14, combined with increased resistance to advancement at the annulus fibrosus, causes the tip of the intradiscal section to bend relative to the longitudinal axis of introducer 12 when the intradiscal section contacts the inner wall of the annulus fibrosus 122. Catheter 14 is navigated along inner wall 22 of annulus fibrosus 122 to selected site(s) of inner wall 22 or within nucleus pulposus 120.

The distal portion 28 of intradiscal section 16 is designed to be incapable of piercing the annulus fibrosus 122. The inability of distal portion 28 to pierce the annulus can be the result of either the shape of the tip 29 or flexibility of distal portion 28, or both. The tip 29 is considered sufficiently blunt when it does not penetrate the annulus fibrosus but is deflected back into the nucleus pulposus or to the side around the inner wall of the annulus when the tip 29 is advanced. The tip can be made with a freely rotating ball. This embodiment provides not only a blunt surface but also a rolling contact to facilitate navigation.

Many percutaneous and endoscopic instruments designed for other purposes can be adapted for use in this invention. This permits other functions to be performed at the desired location after the catheter is advanced to that position. For example, cutting edges and sharp points can be present in the distal portion 28 if they can be temporarily masked by a covering element. However, such devices must be sufficiently flexible and thin to meet the design characteristics described in this specification.

In another embodiment an introducer 12 pierces the skin and reaches an exterior of annulus fibrosus 122. A rigid and sharp trocar is then advanced through introducer 12, to pierce annulus fibrosus 122 and enter the disc. The trocar is then removed, and catheter 14 is advanced through a distal end of introducer 12, following the path created by the trocar in annulus fibrosus 122 beyond the end of the introducer. In such cases, the introducer is outside the annulus fibrosus 122 and only the catheter with its guidable distal portion 16 is present inside the disc. The physician can manipulate the proximal portion 15 of the catheter to move the distal portion of the catheter to a selected location for applying thermal energy to the annulus fibrosus 122.

Catheter 14 is not always pre-bent as shown in FIG. 3(a), but optionally can include a biased distal portion 28 if desired. "Pre-bent" or "biased" means that a portion of the catheter (or other structural element under discussion) is made of a spring-like material that is bent in the absence of external stress but which, under selected stress conditions (for example, while the catheter is inside the introducer), is linear. Such a biased distal portion can be manufactured from either spring metal or superelastic memory material (such as Tinel® nickel-titanium alloy, Raychem Corp., Menlo Park, Calif.). The introducer (at least in the case of a spring-like material for forming the catheter) is sufficiently strong to resist the bending action of the bent tip and maintain the biased distal portion in alignment as it passes through the introducer. Compared to unbiased catheters, a catheter with a biased distal portion 28 encourages advancement of intradiscal section 16 substantially in the direction of the bend relative to other lateral directions as shown by the bent location of intradiscal section 16 indicated by dashed lines in FIG. 3(a). Biasing the catheter tip also further decreases likelihood that the tip 29 will be forced through the wall of the annulus fibrosus under the pressure being used to advance the catheter.

In addition to providing a catheter tip that is biased prior to insertion into an introducer, a catheter tip can be provided that is deflected by mechanical means, such as a wire attached to one side of the tip that deflects the tip in the desired direction upon application of force to the proximal end of the deflection wire. Any device in which bending of the tip of a catheter of the invention is controlled by the physician is "actively steerable." In addition to a tip that is actively steerable by action of a wire, other methods of providing a bending force at the tip can be used, such as hydraulic pressure and electromagnetic force (such as heating a shaped memory alloy to cause it to contract). Any of a number of techniques can be used to provide selective bending of the catheter in one lateral direction.

Referring now to FIG. 5(a), a guiding mandrel 32 can be included both to add rigidity to the catheter and to inhibit movement of catheter 14 in the inferior and superior directions while positioned and aligned in the disc plane of a nucleus pulposus 120. This aids the functions of preventing undesired contact with a vertebra and facilitating navigation. The mandrel can be flattened to encourage bending in a plane (the "plane of the bend") orthogonal to the "flat" side of the mandrel. "Flat" here is a relative term, as the mandrel can have a D-shaped cross-section, or even an oval or other cross-sectional shape without a planar face on any part of the structure. Regardless of the exact configuration, bending will preferentially occur in the plane formed by the principal longitudinal axis of the mandrel and a line connecting the opposite sides of the shortest cross-sectional dimension of the mandrel (the "thin" dimension). To provide sufficient resistance to the catheter bending out of the desired plane while encouraging bending in the desired plane, it is preferred to provide a minimum 1.25:1 ratio of "thickest" to "thinnest" cross-sectional dimensions along at least a portion of the intradiscal section. The maximum ratio is 20:1, with the preferred ratio being between 1.5:1 and 16:3, more preferably between 2:1 and 3.5:1. These ratios are for a solid mandrel and apply to any material, as deflection under stress for uniform solids is inversely proportional to the thickness of the solid in the direction (dimension) in which bending is taking place. For other types of mandrels (e.g., hollow or non-uniform), selection of dimensions and/or materials that provide the same relative bending motions under stress are preferred.

A catheter of the present invention is designed with sufficient torsional strength (resistance to twisting) to prevent undesired directional movement of the catheter. Mandrels formed from materials having tensile strengths in the range set forth in the examples of this specification provide a portion of the desired torsional strength. Other materials can be substituted so long as they provide the operational functions described in the examples and desired operating parameters.

While the mandrel can provide a significant portion of the column strength, selective flexibility, and torsional strength of a catheter, other structural elements of the catheter also contribute to these characteristics. Accordingly, it must be kept in mind that it is the characteristics of the overall catheter that determine suitability of a particular catheter for use in the methods of the invention. For example, a mandrel that does not have sufficient torsional strength when acting alone can be combined with another element, such as anti-twisting outer sheath 40 or inserting/advancing a second mandrel, to provide a catheter of the invention. Similarly, components inside the catheter, such as a heating element or potting compound, can be used to strengthen the catheter or provide directional flexibility at the locations of these elements along the catheter.

It is not necessary that the guiding mandrel 32 be flattened along its entire length. Different mandrels can be designed for different sized discs, both because of variations in disc sizes from individual to individual and because of variations in size from disc to disc in one patient. The bendable portion of the mandrel is preferably sufficient to allow intradiscal portion 16 of the catheter to navigate at least partially around the circumference of the inner wall of the annulus fibrosus (so that the operational functions of the catheter can be carried out at desired location(s) along the inner wall of the annulus fibrosus). Shorter bendable sections are acceptable for specialized instruments. In most cases, a flattened distal portion of the mandrel of at least 12 mm, preferably 25 mm, is satisfactory. The flattened portion can extend as much as the entire length of the mandrel, with some embodiments being flattened for less than 15 cm, in other cases for less than 8 cm, of the distal end of the guide mandrel.

In preferred embodiments the guide mandrel or other differential bending control element is maintained in a readily determinable orientation by a control element located at the proximal end of the catheter. The orientation of the direction of bending and its amount can be readily observed and controlled by the physician. One possible control element is simply a portion of the mandrel that extends out of the proximal end of the introducer and can be grasped by the physician, with a shape being provided that enables the physician to determine the orientation of the distal portion by orientation of the portion in the hand. For example, a flattened shape can be provided that mimics the shape at the distal end (optionally made larger to allow better control in the gloved hand of the physician, as in the handle 11 of FIG. 3(b)). More complex proximal control elements capable of grasping the proximal end of the mandrel or other bending control element can be used if desired, including but not limited to electronic, mechanical, and hydraulic controls for actuation by the physician.

The guide mandrel can also provide the function of differential flexibility by varying the thickness in one or more dimensions (for example, the "thin" dimension, the "thick" dimension, or both) along the length of the mandrel. A guide mandrel that tapers (becomes gradually thinner) toward the distal tip of the mandrel will be more flexible and easier to bend at the tip than it is at other locations along the mandrel. A guide mandrel that has a thicker or more rounded tip than more proximal portions of the mandrel will resist bending at the tip but aid bending at more proximal locations. Thickening (or thinning) can also occur in other locations along the mandrel. Control of the direction of bending can be accomplished by making the mandrel more round, i.e., closer to having 1:1 diameter ratios; flatter in different sections of the mandrel; or by varying the absolute dimensions (increasing or decreasing the diameter). Such control over flexibility allows instruments to be designed that minimize bending in some desired locations (such as the location of connector of an electrical element to avoid disruption of the connection) while facilitating bending in other locations (e.g., between sensitive functional elements). In this manner, a catheter that is uniformly flexible along its entire length, is variably flexible along its entire length, or has alternating more flexible and less flexible segments, is readily obtained simply by manufacturing the guide mandrel with appropriate thickness at different distances and in different orientations along the length of the mandrel. Such a catheter will have two or more different radii of curvature in different segments of the catheter under the same bending force.

In some preferred embodiments, the most distal 3 to 40 mm of a guide mandrel is thinner relative to central portions of the intradiscal section to provide greater flexibility, with the proximal 13 to 40 mm of the intradiscal section being thicker and less flexible to add column strength and facilitate navigation.

The actual dimensions of the guide mandrel will vary with the stiffness and tensile strength of the material used to form the mandrel. In most cases the mandrel will be formed from a metal (elemental or an alloy) or plastic that will be selected so that the resulting catheter will have characteristics of stiffness and bending that fall within the stated limits. Additional examples of ways to vary the stiffness and tensile strength include transverse breaks in a material, advance of the material so that it "doubles up," additional layers of the same or different material, tensioning or relaxing tension on the catheter, and applying electricity to a memory metal.

As illustrated in FIG. 5(b), in some embodiments of an apparatus of the invention, guiding mandrel is combined with at least a portion of the catheter 14 to form a structure which provides the functions of both, a wall/mandrel 41. In this figure, the wall/mandrel 41 of catheter 14 can be varied in dimensions as described in the previous section of this specification directed to a separate mandrel, with the same resulting changes in function. For example, changing the thickness of the wall/mandrel 41 that functions as the mandrel portion changes the flexibility and preferred direction of bending of the catheter. In many cases, the wall/mandrel 41 will be thinner than other portions of the catheter wall 33 so that wall/mandrel 41 controls bending. Alternatively, wall/mandrel 41 can be formed of a different material than the other portions 33 of the catheter walls (i.e., one with a lower tensile and/or flexural strength) in order to facilitate bending.

Returning now to FIG. 5(a), the guiding mandrel 32 will generally be located in the interior of catheter 14, where it shares space with other functional elements of the catheter. For example and as shown in FIG. 5(a), thermal energy delivery device lumen 34 can receive any of a variety of different couplings from an energy source 20 to a thermal energy delivery device (functional element) further along the catheter, including but not limited to a wire or other connector between thermal energy elements. Alternatively or concurrently, hollow lumens for delivery or removal of a fluid or solid connectors for application of a force to a mechanical element can be present, so no limitation should be placed on the types of energy, force, or material transporting elements present in the catheter. These are merely some of the possible alternative functional elements that can be included in the intradiscal portion of the catheter. Accordingly, a general description will now be given of some of the possible functional elements.

Since the purpose of the inventive catheter is to repair circumferential bulges in a disc by operation of the instrument at that location inside the disc, a functional element is provided in or on the catheter to carry out that purpose.

Non-limiting examples of functional elements include any element capable of aiding diagnosis, delivering energy, or delivering or removing a material from a location adjacent the element's location in the catheter, such as an opening in the catheter for delivery of a fluid or for suction, a thermal energy delivery device (heat source), a mechanical grasping tool for removing or depositing a solid, a cutting tool (which includes all similar operations, such as puncturing), a sensor for measurement of a function (such as electrical resistance, temperature, or mechanical strength), or a functional element having a combination of these functions.

The functional element can be at any location in the intradiscal portion of the catheter, depending on its intended use. Multiple functional elements can be present, such as multiple functional elements of different types (e.g., a heat source and a temperature sensor) or multiple functional elements of the same type (e.g., multiple heat sources spaced along the intradiscal portion).

One of the possible functional elements present on intradiscal section 16 is a thermal energy delivery device 18. A variety of different types of thermal energy can be delivered including but not limited to resistive heat, radiofrequency (RF), coherent and incoherent light, microwave, ultrasound and chemically induced exothermic heat reactions. In one embodiment, thermal energy delivery device 18 is positioned proximal to the distal portion of intradiscal section 16 so that there is no substantial delivery of energy at the distal portion, which can then perform other functions without being constrained by being required to provide energy (or resist the resulting heat).

Some embodiments have an interior infusion lumen 36. Infusion lumen 36 is configured to transport a variety of different mediums including but not limited to electrolytic solutions (such as normal saline), contrast media (such as Conray meglumine iothalamate), pharmaceutical agents, disinfectants, filling or binding materials such as collagens or cements, chemonucleolytic agents and the like, from a reservoir exterior to the patient to a desired location within the disc. Further, infusion lumen 36 can be used as an aspiration lumen to remove nucleus material or excess liquid or gas (naturally present, present as the result of a liquefying operation, or present because of prior introduction) from the interior of a disc. When used to transport a fluid for irrigation of the location within the disc, the infusion lumen is sometimes referred to as an irrigation lumen. Infusion lumen 36 can be coupled to medium reservoir 21 through the catheter (see FIG. 3(a)).

Included in the particular embodiment shown in FIG. 5(a) is one or more sensor lumens 42. An example is a wire connecting a thermal sensor at a distal portion of the catheter to control elements attached to a connector in the proximal handle 11 of the catheter.

Also included in the embodiment shown in FIG. 5(a) is an optional energy directing device 43 including but not limited to a thermal reflector, an optical reflector, thermal insulator, or electrical insulator. Energy directing device 43 is configured to limit thermal and/or electromagnetic energy delivery to a selected site of the disc and to leave other sections of the disc substantially unaffected. Energy directing device 43 can be positioned on an exterior surface of catheter intradiscal section 16 and/or catheter 14 as well as in an internal portion of the catheter intradiscal section 16 and/or catheter 14. For example, the energy can be directed to the bulging wall of the annulus and to shrink the collagen component of the annulus, while the nucleus is shielded from excess heat. Alternatively, a strip of energy transmitting material may be included on one side of the intradiscal section for directional heating.

In one embodiment, catheter intradiscal section 16 and/or distal portion 28 are positionable to selected site around and/or adjacent to inner wall 22 of annulus fibrosus 122 for the delivery of therapeutic and/or diagnostic agents including but not limited to, electromagnetic energy, electrolyte solutions, contrast media, pharmaceutical agents, disinfectants, collagens, cements, chemonucleolytic agents and thermal energy. Intradiscal section 16 is navigational and can reach the posterior, the posterior lateral, the posterior medial, anterior lateral, and anterior medial regions of the annulus fibrosus, as well as any selected section on or adjacent to inner wall 22.

In a preferred embodiment, intradiscal section 16 is positioned adjacent to the entire posterior wall of the disc. Sufficient thermal energy can then be delivered, for example, to selectively heat the posterior annulus to shrink the collagen component of the wall without undue damage to other portions of the intervertebral disc, particularly the nucleus. These actions help stiffen the annulus.

In the preferred embodiment of FIG. 5(a), markings 38 are visible on the portion of the catheter that is located during normal operation outside the body being acted upon, particularly for embodiments in which the proximal end of the catheter is designed to be directly manipulated by the hand of the physician. Advancement of the catheter into the introducer will advance the markings into the introducer, thereby showing how far the catheter has been advanced into the nucleus. Such a visible marking 38 can be positioned on an exterior surface of the catheter or can be present on an interior surface and visible through a transparent outer covering or sheath. Preferred are visible markings every centimeter to aid the physician in estimating the catheter tip advancement.

If desired, visible markings can also be used to show twisting motions of the catheter to indicate the orientation of the bending plane of the distal portion of the catheter. It is preferred, however, to indicate the distal bending plane by the shape and feel of the proximal end of the catheter assembly. The catheter can be attached to or shaped into a handle 11 that fits the hand of the physician and also indicates the orientation of the distal bending plane. Both the markings and the handle shape thus act as control elements to provide control over the orientation of the bending plane; other control elements, such as plungers or buttons that act on mechanical, hydrostatic, electrical, or other types of controls, can be present in more complex embodiments of the invention.

Additionally, a radiographically opaque marking device can be included in the distal portion of the catheter (such as in the tip or at spaced locations throughout the intradiscal portion) so that advancement and positioning of the intradiscal section can be directly observed by radiographic imaging. Such radiographically opaque markings are preferred when the intradiscal section is not clearly visible by radiographic imaging, such as when the majority of the catheter is made of plastic instead of metal. A radiographically opaque marking can be any of the known (or newly discovered) materials or devices with significant opacity. Examples include but are not limited to a steel mandrel sufficiently radio-opaque to be visible on fluoroscopy, a tantalum/polyurethane tip, a gold-plated tip, bands of platinum, stainless steel or gold, soldered spots of gold and polymeric materials with radiographically opaque filler such as barium sulfate. A resistive heating element or an RF electrode(s) may provide sufficient radio-opacity in some embodiments to serve as a marking device.

A sheath 40 can optionally be positioned around catheter 14. Sheath 40 provides a flexible surface that is smooth and provides for easy introduction into a selected area within the disc. Sheath 40 can be made of a variety of different materials including but not limited to polyester, rayon, polyimide, polyurethane, polyethylene, polyamide and silicone. When visible markings are present to indicate the advancement of the catheter, either the sheath carries the markings, or the sheath is clear to reveal markings underneath.

In one preferred embodiment, thermal energy delivery device 18 is a resistive heating device. As illustrated in FIG. 6, a heating coil 46 is positioned around an exterior of catheter 14. The heating element 46 need not be in the shape of a coil. Heating element 46 is powered by a direct current source 20 (and less preferably a source of alternating current). Heating element is made of a material that acts as a resistor. Suitable materials include but are not limited to stainless steel, nickel/chrome alloys, platinum, ferrite, and the like.

Preferably, the heating element is inside the intradiscal section of catheter 14 (FIG. 8). The resistive material is electrically insulated and substantially no current escapes into the body. With increasing levels of current, element 46 heats to greater temperature levels. Additionally, a circuit can be completed substantially entirely at intradiscal section 16 and a controllable delivery of thermal energy is achieved. In one embodiment, 2 watts pass through heating element 46 to produce a temperature of about 55° C. in a selected target such as a degenerate annulus, 3 watts produces 65° C., 4 watts produces 75° C., and so on.

In another embodiment, thermal energy delivery device 18 is a radiofrequency electrode, such as a band or coil. As illustrated in FIG. 6, RF element 46 is positioned on an exterior of catheter 14. RF element 46 is powered by an RF generator. The electrode is made of suitable materials including but not limited to stainless steel or platinum. The RF electrode is located on intradiscal section of catheter 14. Increasing levels of current conducted into disc tissue heat that tissue to greater temperature levels. A circuit can be completed substantially entirely at intradiscal section 16 (bipolar device) or by use of a second electrode attached to another portion of the patient's body (monopolar device). In either case, a controllable delivery of RF energy is achieved.

In another embodiment sufficient energy is delivered to the intervertebral disc to heat and shrink and stiffen the collagen component of the annulus but not ablate tissue adjacent to catheter 14.

For a resistive heater, the amount of thermal energy delivered to the tissue is a function of (i) the amount of current passing through heating element 46, (ii) the length, shape, and/or size of heating element 46, (iii) the resistive properties of heating element 46, (iv) the gauge of heating element 46, and (v) the use of cooling fluid to control temperature. All of these factors can be varied individually or in combination to provide the desired level of heat. Power supply 20 associated with heating element 46 may be battery based. Catheter 14 can be sterilized and may be disposable.

Referring now to FIG. 7, a thermal sensor 48 may be positioned in an interior location of catheter 14. In another embodiment, thermal sensor 48 is positioned on an exterior surface of catheter 14. A thermal sensor can be used to control the delivery of energy to thermal energy delivery device 18. A potting material can be used to fix the position of thermal sensor 48 and provide a larger area from which to average the measured temperature. Thermal sensor 48 is of conventional design, including but not limited to a thermistor; T type thermocouple with a copper constantan junction; J type, E type, and K type thermocouples; fiber optics; resistive wires; IR detectors; and the like. Optionally, there may be a lumen 42 for the thermal sensor connection.

As illustrated in FIG. 8, sheath 40 may be used to cover resistive heating element 46. A plurality of resistive heating elements 46 can be used (FIG. 9) in a catheter of the invention.

Referring now to the embodiment shown in FIG. 10, thermal energy delivery device 18 comprises one or more resistive heating elements 46 coupled to a resistive heating energy source. Resistive heating elements 46 are positioned along intradiscal section 16 at locations where they controllably deliver thermal energy to selected structures, such as weak degenerate areas in the annulus. Resistive heating elements 46 can be segmented and multiplexed so that only certain resistive heating elements, or combinations of resistive heating elements are activated at any one particular time. Thermal sensor 48 can be positioned between resistive heating elements 46 and/or at an exterior or interior location of catheter 14. In the embodiment illustrated in FIG. 10, catheter 14 can be prepared with a wound helical structural element 49 to increase flexibility and minimize kinking. However, other structures and geometries are suitable for catheter 14, including but not limited to a substantially smooth surface (and specifically including the devices using an internal guide mandrel as previously described). For example, a sheath can be provided over the heating element, and the guiding mandrel inside the coil can be encapsulated in silicone potting material. The tubing flexibility and the silicone potting material prevent kinking. Additionally, sheath 40 can be positioned around catheter 14 and also around resistive heating elements 46 to afford a substantially smooth surface. Resistive heating elements 46 can be at least partially covered by a thermally insulating material, for example, along one side of the catheter, to selectively heat disc tissue on the opposite side.

Referring now to FIGS. 11 and 12, an open or closed loop feedback system 52 couples sensors 48 to energy source 20. As illustrated in FIG. 10, thermal energy delivery device 18 is a resistive heating element 46. It will be appreciated that the embodiments illustrated in FIGS. 10 and 11 are readily adaptable to other thermal energy delivery sources (e.g., for radiofrequency energy, the resistive heating element is replaced with insulated RF probe(s) and the energy source is an RF generator).

The temperature of the tissue or of element 46 (FIG. 10) is monitored by sensors 48, and the output power of energy source 20 adjusted accordingly. The physician can, if desired, override control system 52. A microprocessor can be included and incorporated in the closed or open loop system to switch power on and off, as well as to modulate the power. The closed loop system utilizes a microprocessor to serve as a controller 54 which acts to monitor the temperature and adjust the power accordingly. Alternatives to the microprocessor are, for example, analog control circuitry and a logic controller.

With the use of sensors 48 and feedback control system 52, a tissue adjacent to resistive heating elements 46 can be maintained at a desired temperature for a selected period of time without aberrant high temperature fluctuations. Each resistive heating element 46 can be connected to separate control and power supply resources, which generate an independent output for each resistive heating element 46. For example, a desired thermal output can be achieved by maintaining a selected energy at resistive heating elements 46 for a selected length of time.

When a resistive heating element 46 is used, current delivered through resistive heating element 46 can be measured by current sensor 56. Voltage can be measured by voltage sensor 58. Resistance and power are then calculated at power calculation device 60. These values can then be displayed at user interface and display 62. Signals representative of power and resistance values are received by a controller 54.

A control signal is generated by controller 54 that is related to the voltage and current. The control signal is used by power circuits 66 to adjust the power output in an appropriate amount in order to maintain the desired power delivered at respective resistive heating elements 46.

In a similar manner, temperatures detected at sensors 48 provide feedback for maintaining a selected power. The actual temperatures are measured at temperature measurement device 68, and the temperatures are displayed at user interface and display 62. A control signal is generated by controller 54 that is related to the actually measured temperature and a desired temperature. The control signal is used by power circuits 66 to adjust the power output in an appropriate amount in order to maintain the desired temperature delivered at the respective sensor 48. A multiplexer can be included to measure current, voltage, and temperature at the sensors 48, 56 and 58, so that appropriate energy can be delivered to resistive heating elements 46.

Controller 54 can be a digital or analog controller or a computer with software. When controller 54 is a computer, it can include a CPU coupled through a system bus. Included in this system can be a keyboard, a disc drive or other non-volatile memory system, a display, and other peripherals, as are known in the art. Also coupled to the bus can be a program memory and a data memory.

User interface and display 62 includes operator controls and a display. Controller 54 can be coupled to imaging systems well known in the art.

The output of current sensor 56 and voltage sensor 58 is used by controller 54 to maintain a selected power level at resistive heating elements 46. A predetermined profile of power delivered can be incorporated in controller 54, and a preset amount of energy to be delivered can also be profiled.

Circuitry, software, and feedback to controller 54 result in process control and in the maintenance of the selected power that is independent of changes in voltage or current. Control can include (i) the selected power and (ii) the duty cycle (wattage and on-off times). These process variables are controlled and varied while maintaining the desired delivery of power independent of changes in voltage or current, based on temperatures monitored at sensors 48.

In the embodiment shown, current sensor 56 and voltage sensor 58 are connected to the input of an analog amplifier 70. Analog amplifier 70 can be a conventional differential amplifier circuit for use with sensors 48, 56 and 58. The output of analog amplifier 70 is sequentially connected by an analog multiplexer 72 to the input of A/D converter 74. The output of analog amplifier 70 is a voltage which represents the respective sensed parameters. Digitized amplifier output voltages are supplied by A/D converter 74 to microprocessor 54. Microprocessor 54 may be a type 68HCII available from Motorola. However, it will be appreciated that any suitable microprocessor or general purpose digital or analog computer can be used to the parameters of temperature, voltage or current.

Microprocessor 54 sequentially receives and stores digital representations of temperature. Each digital value received by microprocessor 54 corresponds to different parameters.

Calculated power and temperature values can be indicated on user interface and display 62. Alternatively, or in addition to the numerical indication of power, calculated power values can be compared by microprocessor 54 with power limits. When the values exceed predetermined power or temperature values, a warning can be given on user interface and display 62, and additionally, the delivery of electromagnetic energy can be reduced, modified or interrupted. A control signal from microprocessor 54 can modify the power level supplied by energy source 20.

In preferred embodiment of the invention, the materials that make up the various parts of an apparatus of the invention have the following characteristics:

    __________________________________________________________________________             Tensile                         Geometry (height,                              Strength in                                                                          %    Conductivity                                                                            Resistivity                                                                          Melt temp.                                                                           width, and/or dia.)                    Component                                                                              MPa   Elongation                                                                          cal/cm.sup.2 /cm/sec/° C.                                                        nΩ*m                                                                           ° C.                                                                          in mm                                  __________________________________________________________________________     Mandrel 600-2100                                                                             5-100                                                                               N/A      N/A   N/A   height 0.2-2.3                                                                 width 0.05-0.5                         Heating Element                                                                        300 min.                                                                             20 (min.)                                                                           .025-0.2 500-1500*                                                                            N/A   0.05-0.5 dia.                          Conductor                                                                              N/A   N/A  .2-1.0   150 max.*                                                                            N/A   0.1-0.5 dia.                           Wire                                                                           Plastic sheath                                                                         N/A   25 (min.)                                                                           N/A      N/A   80° (min.)                                                                    0.05-0.02                                                                      thickness                              __________________________________________________________________________

Another preferred characteristic is that the minimum ratio of heating element resistivity to conductor wire resistivity is 6:1; the preferred minimum ratio of guiding mandrel height to guiding mandrel width is 2:1. Tensile strength and % elongation can be measured according to ASTME8 (tension test of metallic materials). Conductivity and resistivity can be determined by procedures to be found in ASTM Vol. 2.03 for electrothermal properties.

A particularly preferred embodiment of a catheter of the invention can be prepared using a covering sheath of polyimide with an outside diameter of 1 mm and a wall thickness of 0.05 mm. Such a sheath provides a significant fraction of the stiffness and torsional strength appropriate for the catheter. Internal to the polyimide sheath and in the intradiscal section of the catheter is a heating coil of insulated nickel/chromium wire that has an outside diameter that matches the interior diameter of the polyimide sheath. This heating coil provides both heat and additional stiffness to the assembly. Also internal to the polyimide sheath on each side of the coil (longitudinally) is a 0.10 mm-walled, 304 stainless-steel, metallic band whose outer diameter matches the inner diameter of the sheath, the distal band having a hemispherical end that exits the end of the polyimide sheath and creates a blunt tip 29 at the end of the catheter. These bands provide enhanced radio-opacity for fluoroscopic visualization, as well as some of the stiffness of the assembled apparatus. Proximal to the proximal metallic band and internal to the sheath is an additional polyimide tube 47 that increases the stiffness of the catheter in the region that transitions from the intradiscal section containing the coil to the rigid proximal section. Proximal to the second polyimide tube and internal to the sheath is a 304 stainless steel hypodermic tube with an outside diameter matching the inside diameter of the polyimide sheath and a wall thickness of 0.1 mm. This combination provides the rigidity needed for a physician to advance the distal portion of the device inside a nucleus pulposus and provides tactile force feedback from the tip to the physician.

In some embodiments, inside the bands, coil, hypodermic tube, and both the polyimide sheath and internal polyimide tube is a guiding mandrel that extends from a proximal handle to the catheter tip. In one embodiment, this mandrel is 0.15 mm by 0.5 mm and formed from 304 stainless steel. In another embodiment, it is a 0.3 mm diameter 304 stainless steel wire, with the distal 2.5 cm flattened to 0.2 mm by 0.5 mm.

Inside the center of the heating coil is a T-type thermocouple potted with cyanoacrylate adhesive into a polyimide sheath and located alongside the mandrel. The thermocouple wire travels through the coil and hypodermic tube to the handle at the proximal end of the apparatus. Two copper conductor wires (36 gauge insulated with polyimide) are soldered to the heating coil and pass through the hypodermic tube and handle to the proximal handle's electrical connector, which allows a power supply and feedback controls to be connected to electrical elements in the catheter. One embodiment has the handle fitted with a 1-3-meter-cable extension ending in an electrical connector to eliminate the need for a connector in the handle. This design reduces weight (from connector elements) on the proximal end and increases the physician's tactile feedback during device manipulation.

The entire inside of the catheter in one embodiment is encapsulated with a silicone material which removes air (which would insulate the heat created by the heating coil) and helps support the polyimide sheath to prevent collapse (i.e., increases stiffness). Instead of the silicone, another embodiment uses an epoxy which remains flexible after curing. Strain relief is provided between the catheter body and the handle with an elastomeric boot. The distal end of the catheter is pre-bent 15-30° off the longitudinal axis of the catheter at about 5-10 mm from the distal tip.

The catheter in one embodiment carries visible markings 38 on the hypodermic tube (with the markings being visible through the polyimide sheath) to indicate distance of insertion of the catheter into an introducer and/or distance that the distal end of the catheter extends out of the introducer into a disc. The catheter is also marked both visually and with tactile relief on its handle to indicate the direction of bending of the pre-bent tip and biased stiffness.

The guidable apparatus described herein can be used in any of a number of methods to treat annular bulges. Specific methods that can be carried out with an apparatus of the invention will now be described.

Degenerative discs with circumferential bulges can be treated non-destructively without desiccation or charring of tissues. Such bulges can be ameliorated by shrinking the collagen component of the annulus. To do that, the disc adjacent to the fissure is typically heated to a temperature in the range of about 45-70° C. Thermal shrinking of collagen also facilitates ingrowth of more collagen, which further increases annular stiffness. If necessary, the area of the bulge can be reinforced with filler (non-adhesive material that blocks the opening), bonding material (adhesives) or other such sealants.

In some methods of the invention, bonding materials such as collagen, albumin, fibrinogen cements are delivered to the weak area. Collagen from a variety of sources can be used (e.g., bovine extracted collagen from Semex Medical, Frazer, Pa., or human recombinant collagen from Collagen Corp., Palo Alto, Calif.). The collagen is injected dissolved or as a fine slurry, after which it is allowed to set or may be heated in situ where it provides a matrix for normal collagen disposition by the body.

A variety of different materials can also be delivered to the disc, including but not limited to electrolyte solutions (i.e. normal saline), contrast media (e.g., Conray meglumine iothalamate), pharmaceutical agents (such as the steroid methylprednisolone sodium succinate available from Pharmacia & Upjohn, Kalamazoo, Mich., and nonsteroidal anti-inflammatory drugs), chemonucleolytic enzyme (e.g., chymopapain), hydrogel (such as disclosed in U.S. Pat. No. 4,478,822), osteoinductive substances (e.g., BMP, see U.S. Pat. No. 5,364,839), chondrocyte inductive substance (e.g., TGF-β) and the like. The materials are delivered via the catheter and/or introducer to the disc. Preferably, however, when precision placement of the material is necessary or desired, the delivery method uses the apparatus described above, especially when delivery to the posterior, posterior lateral, or posterior medial region of the disc is desired. The materials may be administered simultaneously or sequentially, such as beginning with an electrolyte solution (which helps the physician view the pathology) and following with products to reinforce the degenerate annulus.

The delivered material can be fixed in position with an adhesive, with a hydrogel that is liquid at room temperature but gels at body temperature, with naturally occurring processes (such as interaction of fibrinogen and thrombin) within the disc, or by heating the disc as described in more detail below.

If desired because intradiscal pressure is excessive, chymopapain can be injected through the subject catheter. Chymopapain splits side chains off proteoglycan molecules, thereby decreasing their ability to hold water. The disc gradually decreases in size. A typical dose is 0.75 to 1.0 ml (2000 pKat/ml).

In this embodiment, thermal energy is delivered to select sections of the disc in an amount that does not char or vaporize tissue. Only sufficient thermal energy is delivered to the disc to change its biochemical and/or biomechanical properties without structural degradation of tissue. If the roll is fully circumferential, heat is applied at successive locations around the entire circumference, a procedure heretofore not possible. Otherwise, the catheter is positioned, and heat is applied to particular areas in need of treatment.

All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

The foregoing description of preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to practitioners skilled in this art. It is intended that the scope of the invention be defined by the following claims and their equivalents. 

What is claimed is:
 1. A method of treating an intervertebral disc comprising:providing a catheter having an intradiscal section with at least one energy delivery device adjacent a distal end of the catheter and a proximal end for externally guiding the distal end of the catheter within an intevertebral disc; positioning the energy delivery device at a selected location of the annulus by applying a force longitudinally to the proximal end of the catheter which is sufficient to advance the intradiscal section through a nucleus pulposus and around an inner wall of an annulus fibrosus, but which force is insufficient for the intradiscal section to puncture the annulus fibrosus; and causing the energy delivery device to supply sufficient energy to the selected location to stiffen the annulus.
 2. The method of claim 1, wherein positioning the energy delivery device further comprises twisting the proximal end of the catheter.
 3. The method of claim 1, advancing the catheter comprises advancing the catheter in a plane of the disc.
 4. The method of claim 1, wherein positioning effectively locates the energy delivery device at a location selected from the group consisting of a posterior lateral, posterior medial, and anterior medial portion of the annulus fibrosus, or a combination thereof.
 5. The method of claim 1, wherein positioning is preceded byproviding an introducer with a proximal end and a distal end and having an introducer lumen with a distal opening at a terminus of the introducer; inserting the introducer so that the distal end of the introducer is inside the annulus; and slidably positioning the catheter in the introducer lumen.
 6. The method of claim 1, wherein the step of causing the energy delivery device to supply sufficient energy comprises adding energy sufficient to shrink and stiffen the collagen component of the annulus fibrosus.
 7. The method of claim 1, wherein positioning and causing the energy delivery device to supply sufficient energy are repeated at least once.
 8. The method of claim 7, wherein positioning and causing the energy delivery device to supply sufficient energy are repeated until the entire disc circumference is treated.
 9. The method of claim 1, wherein the step of providing a catheter further includes providing a catheter with a lumen capable of delivering or aspirating a material.
 10. The method of claim 9 comprising the additional step of placing a material in the disc.
 11. The method of claim 10 wherein the step of placing the material comprises placing a material selected from the group consisting of irrigation solutions, contrast media, pharmaceutical agents, chemonucleolytic enzymes, hydrogel, osteoinductive substances, chondrocyte-inductive substances, cements, adhesives, collagen, fibrinogen and thrombin, and combinations thereof.
 12. The method of claim 11, wherein the step of placing a material is followed by the step of heating the material to seal it in place.
 13. The method of claim 1, wherein the intradiscal section has a bending stiffness as measured in Taber stiffness units between about 2-400 units in a desired bending plane.
 14. The method of claim 1, wherein the intradiscal section has a bending stiffness as measured in Taber stiffness units between about 3-150 units in a desired bending plane.
 15. The method of claim 1, wherein the intradiscal section has a bending stiffness as measured in Taber stiffness units between about 4-30 units in a desired bending plane.
 16. The method of claim 15, wherein the proximal end of the catheter has a column strength between about 0.2-7 kg.
 17. The method of claim 15, wherein the proximal end of the catheter has a column strength between about 0.7-4 kg.
 18. The method of claim 1, wherein the intradiscal section has a column strength between about 0.05-4 kg.
 19. The method of claim 18, wherein the proximal end of the catheter has a column strength between about 0.1-25 kg.
 20. The method of claim 18, wherein the proximal end of the catheter has a column strength between about 0.2-7 kg.
 21. The method of claim 18, wherein the proximal end of the catheter has a column strength between about 0.7-4 kg.
 22. The method of claim 1, wherein the intradiscal section has a column strength between about 0.05-2 kg.
 23. The method of claim 22, wherein the proximal end of the catheter has a column strength between about 0.1-25 kg.
 24. The method of claim 22, wherein the proximal end of the catheter has a column strength between about 0.2-7 kg.
 25. The method of claim 22, wherein the proximal end of the catheter has a column strength between about 0.7-4 kg.
 26. The method of claim 1, wherein the energy delivery device is capable of delivering a controlled amount of energy to the selected location such that no vaporization occurs at or near the selected location when energy is delivered by the energy delivery device.
 27. The method of claim 1, wherein the energy delivery device is capable of delivering a controlled amount of energy to the selected location such that no material other than water is removed at or near the selected location when energy is delivered by the energy delivery device.
 28. The method of claim 1, wherein the energy delivery device is capable of delivering a controlled amount of energy to the selected location such that no destructive lesion is formed on a disc at or near the selected location when energy is delivered by the energy delivery device. 